Vacuum-actuated wastegate

ABSTRACT

Embodiments for vacuum generation are provided. In one example, a method for an engine including a turbocharger having a compressor driven by a turbine comprises generating vacuum via compressor bypass flow through an ejector, and applying vacuum from the ejector to a wastegate actuator. In this way, vacuum produced via boosted engine operation may be used to actuate the wastegate valve.

FIELD

The present disclosure relates to an internal combustion engine.

BACKGROUND AND SUMMARY

Turbochargers may improve engine torque/power output density. Aturbocharger may include a compressor and a turbine connected by a driveshaft, where the turbine is coupled to an exhaust manifold side and thecompressor is coupled to an intake manifold side. In this way, theexhaust-driven turbine supplies energy to the compressor to increase thepressure in the intake manifold (e.g. boost, or boost pressure) and toincrease the flow of air into the engine. The boost may be controlled byadjusting the amount of gas reaching the turbine, for example with awastegate.

Wastegates may be actuated pneumatically, hydraulically, orelectrically. In one example, a wastegate may be actuated via boostpressure produced by the turbocharger. However, it may be advantageousto open the wastegate during low- or no-boost conditions, in order toreduce pumping losses and improve fuel economy. Thus, vacuum-actuatedwastegates have been developed to allow for wastegate control during lowboost conditions. While vacuum-actuated wastegates may provide robustwastegate control during conditions of high engine vacuum, duringhigher-boost conditions, the engine intake manifold vacuum used toprovide vacuum to actuate the wastegate is not available. A separatevacuum pump may be provided to supply the needed vacuum when enginevacuum is not available, thus wasting fuel.

The inventors have recognized the issues with the above approach andoffer a method to at least partly address them. In one embodiment, amethod for an engine including a turbocharger having a compressor drivenby a turbine comprises generating vacuum via compressor bypass flowthrough an ejector, and applying vacuum from the ejector to a wastegateactuator.

In this way, the vacuum resulting from a boost condition both acts as awastegate control signal and is also used to actuate the wastegate. Anejector positioned in the compressor bypass flow may generate vacuumthat is directed to the wastegate actuator. Thus, when excess boost isavailable for vacuum generation via the ejector, the wastegate isopened.

Further, in some examples, vacuum from the intake manifold may also beused to actuate the wastegate, such as when boost pressure is low. Byactuating the wastegate with the vacuum-producing ejector during someconditions and with the intake manifold vacuum under other conditions,fully active wastegate control may be provided, thus increasing fueleconomy. This is in contrast to previous systems, where in a pressureactuated wastegate, pressure is only available during boosted operation,and in a typical vacuum actuated wastegate, vacuum is only availableduring non-boosted operation.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine including an ejectorproviding vacuum to a wastegate actuator according to an embodiment ofthe present disclosure.

FIG. 2 shows the engine of FIG. 1 with additional wastegate actuationmechanisms.

FIG. 3 shows a schematic diagram of an engine including an ejectorproviding vacuum to a wastegate actuator according to another embodimentof the present disclosure.

FIG. 4 shows the engine of FIG. 3 with additional wastegate actuationmechanisms.

FIG. 5 is a flow diagram illustrating a method for generating vacuumaccording to an embodiment of the present disclosure.

FIGS. 6 and 7 are schematic diagrams of an engine with dual ejectormotive flow control provided by a single actuator according toembodiments of the present disclosure.

FIG. 8 is a flow diagram illustrating a method for controlling motiveflow through multiple ejectors with one actuator according to anembodiment of the present disclosure.

FIGS. 9 and 10 illustrate various engine operating parameters withcoordinated control of the dual ejector motive control with the singleactuator.

DETAILED DESCRIPTION

Wastegates may provide boost control by bypassing exhaust around aturbine. To provide wastegate actuation under a variety of engineconditions, the boost pressure acting as a wastegate control signal mayalso be used to generate vacuum to actuate the wastegate. An ejectorpositioned in either the compressor or the turbine bypass flow maygenerate vacuum that is directed to the wastegate actuator.Alternatively, the ejector may be placed between other suitable pressuredifferences in the exhaust conduit, the air conduit, or a combination ofboth. Thus, when excess boost is available for vacuum generation via theejector, the wastegate is opened. To provide for a variable boost limit,a vent valve may be present to vent some or the entire vacuum away fromthe actuator. Further, to actuate the wastegate under low or no boostconditions, the actuator may be provided with intake manifold vacuum,supplied directly from the intake manifold or produced from an ejectorcoupled across the throttle. In this way, the wastegate may bevacuum-actuated under both high and low boost conditions.

FIGS. 1 and 2 are engine diagrams illustrating wastegate actuation withvacuum generated from a boost ejector coupled across a compressor. FIGS.3 and 4 are engine diagrams illustrating wastegate actuation with vacuumgenerated from a boost ejector coupled across a turbine. FIG. 5 is aflow chart illustrating a method for generating vacuum with the systemillustrated in FIG. 2 or FIG. 4.

To provide efficient control of the vacuum generation, the boostejector's motive flow (e.g., ejector coupled across the compressor orturbine) may be controlled by a motive flow control valve incoordination with a motive flow control valve controlling the throttleejector's motive flow. The two motive flow control valves may beactuated by a single actuator. Further, the motive flow control valvecontrolling the ejector coupled across the compressor may act as a surgemargin valve under some conditions, reducing the compressor bypass valveand helping to reduce compressor surge.

FIGS. 6 and 7 are engine diagrams illustrating control of two ejectorsby a single actuator. FIG. 8 is a flow chart illustrating a method forgenerating vacuum with the system illustrated in FIGS. 6 and 7. FIGS. 9and 10 illustrate various engine operating parameters during vacuumgeneration with the two ejectors controlled by a single actuator.

FIG. 1 shows an example engine system 10 including an engine 12. In thepresent example, engine 12 is a spark-ignition engine of a vehicle, theengine including a plurality of cylinders 14, each cylinder including apiston. Combustion events in each cylinder 14 drive the pistons which inturn rotate crankshaft 16, as is well known to those of skill in theart. Further, engine 12 may include a plurality of engine valves, thevalves coupled to the cylinders 14 and controlling the intake andexhaust of gases in the plurality of cylinders 14.

Engine 12 includes an engine intake 23 and an engine exhaust 25. Engineintake 23 includes an air intake throttle 22 fluidly coupled to anengine intake manifold 24 along an intake passage 18. Air may enterintake passage 18 from an air intake system (AIS) including an aircleaner 33 in communication with the vehicle's environment. A positionof throttle 22 may be varied by a controller 50 via a signal provided toan electric motor or actuator included with the throttle 22, aconfiguration that is commonly referred to as electronic throttlecontrol (ETC). In this manner, the throttle 22 may be operated to varythe intake air provided to the intake manifold and the plurality ofcylinders 14. The intake 23 may include a mass air flow sensor 58 (inintake passage 18) and a manifold air pressure sensor 60 (in intakemanifold 24) for providing respective signals MAF and MAP to thecontroller 50.

Engine exhaust 25 includes an exhaust manifold 48 leading to an exhaustpassage 35 that routes exhaust gas to the atmosphere. Engine exhaust 25may include one or more emission control devices 70 mounted in aclose-coupled position. The one or more emission control devices mayinclude a three-way catalyst, lean NOx trap, diesel particulate filter,oxidation catalyst, etc. It will be appreciated that other componentsmay be included in the engine such as a variety of valves and sensors,as further elaborated in herein.

In some embodiments, engine system 10 is a boosted engine system, wherethe engine system further includes a boosting device. In the presentexample, intake passage 18 includes a compressor 90 for boosting anintake aircharge received along intake passage 18. A charge air cooler26 (or intercooler) is coupled downstream of compressor 90 for coolingthe boosted aircharge before delivery to the intake manifold. Inembodiments where the boosting device is a turbocharger, compressor 90may be coupled to, and driven by a turbine 92 in the engine exhaust 25of engine system 10. Further compressor 90 may be, at least in part,driven by an electric motor or crankshaft 16.

An optional bypass passage 28 may be coupled across compressor 90 so asto divert at least a portion of intake air compressed by compressor 90back upstream of the compressor. An amount of air diverted throughbypass passage 28 may be controlled by opening compressor bypass valve(CBV) 30 located in bypass passage 28. By controlling CBV 30, andvarying an amount of air diverted through the bypass passage 28, a boostpressure provided downstream of the compressor can be regulated. Thisenables boost control and surge control.

Similarly, an optional bypass passage 40 may be coupled across turbine92 so to divert at least a portion of exhaust around turbine 92, thuscontrolling turbine speed and hence boost pressure provided to theengine. The amount of exhaust diverted around turbine 92 may becontrolled by opening a wastegate 42 located in bypass passage 40.Wastegate 42 may be moved via a wastegate actuator 44, which may be asolenoid actuator, hydraulic actuator, or in the depicted example, avacuum-driven actuator.

In order to generate vacuum to drive wastegate actuator 44, an ejector80 may be positioned in the compressor bypass flow. As shown, ejector 80is positioned in a separate bypass passage 82 around compressor 90, inparallel with bypass passage 28. However, in some embodiments ejector 80may be located in bypass passage 28. High-pressure intake air from theoutlet of the compressor may flow through ejector 80 (air flow throughthe passages and conduits of FIG. 1 is generally depicted by arrows) andback to the lower-pressure region of the compressor inlet. Vacuumgenerated by ejector 80 may be routed to wastegate actuator 44 viaconduit 84.

Ejector 80 may be an ejector, injector, aspirator, eductor, venturi, jetpump, or similar passive device. Ejector 80 may have an upstream motiveflow inlet via which air enters the ejector, a throat or entraininginlet fluidically communicating with wastegate actuator 44 via conduit84, and a mixed flow outlet via which air that has passed throughejector 80 can exit and be directed to a low-pressure sink, such asintake passage 18 upstream of compressor 90 (e.g., it may be directed tothe inlet of compressor 90). Air flowing through the motive inlet maycreate a low pressure in the ejector 80, thereby creating a low pressurecommunicated to the throat (or entraining inlet) and drawing a vacuum atthe throat. The vacuum at the throat of the ejector draws air fromconduit 84, thus providing vacuum to wastegate actuator 44. To controlair flow through ejector 80, an optional motive flow control valve 86may be located in bypass passage 82, upstream, downstream, or midstreamof the ejector motive flow. Additionally, an optional check valve mayallow wastegate actuator 44 to retain any of its vacuum should thepressures in the ejector's motive inlet and the vacuum actuatorequalize. Such a check valve may utilize further venting valves toprevent the wastegate from opening permanently. In the present example,the ejector is a three port device including a motive inlet, a mixedflow outlet, and a throat/entraining inlet. However, in alternateembodiments of the ejector, a check valve may be integrated into theejector.

Engine system 10 may also include a control system 46 including acontroller 50, sensors 51 and actuators 52. Example sensors includeengine speed sensor 54, engine coolant temperature sensor 56, a mass airflow sensor 58, manifold air pressure sensor 60, compressor inletpressure sensor 32, and throttle inlet pressure sensor 34. Exampleactuators include CBV 30, ejector motive flow control valve 86, throttle22, and engine valves, fuel injectors, and other components notillustrated in FIG. 1. Controller 50 may further include a physicalmemory with instructions, programs and/or code for operating the engine.Example routines executed by controller 50 are shown at FIGS. 5 and 8.

Thus, the system of FIG. 1 provides for a vacuum-actuated wastegatevalve to control boost pressure by adjusting the amount of exhaust thatbypasses a turbocharger turbine. The wastegate actuator may receivevacuum generated by flowing air through an ejector coupled across acompressor of the turbine. In this way, the wastegate valve may beopened based on the level of provided boost (e.g., the amount of airthat is bypassed around the compressor and through the ejector), as theamount of vacuum supplied to the wastegate actuator increases asthrottle inlet pressure (e.g., boost) increases. However, additionalcontrol of the wastegate actuator may be desired. For example, it may bedesired to open the wastegate valve under conditions of low or no boost,in order to increase fuel economy. Additionally, it may be desired toactively control the amount of boost pressure with the wastegateactuator, by selectively supplying vacuum to the wastegate actuator.FIG. 2 illustrates an engine system 200 including the features of FIG. 1plus additional, optional components to provide boost control andwastegate actuation under low boost conditions.

Engine system 200 includes similar features as engine system 10,including the engine 12, compressor 90, turbine 92, ejector 80 supplyingvacuum to wastegate actuator 44, and other components previouslydescribed. Conduit 84, which supplies vacuum from ejector to wastegateactuator 44, is depicted in FIG. 2 as running the entire length fromejector 80 down to actuator 44. In order to provide active boost controlvia actuation of wastegate 42, a vent line 202 may be present in orderto couple conduit 84 to the intake passage 18 upstream of compressor 90.A vent valve 204 may be positioned in vent line 202 or at theintersection of vent line 202 and conduit 84. Vent valve 204 may becontrolled by controller 50 to adjust the amount of vacuum supplied towastegate actuator 44, with excess vacuum being routed back to theintake via the vent line 202. Thus, by controlling vent valve 204,active boost pressure control may be provided.

In order to open wastegate 42 under conditions of little or no boost(e.g., when sufficient vacuum is not generated via ejector 80), vacuummay be routed to wastegate actuator 44 from the intake passage or theintake manifold 24. To provide intake manifold vacuum, a second ejector206 may be coupled across the throttle 22. Second ejector 206 maygenerate vacuum from motive flow of intake air from upstream of thethrottle to downstream of the throttle. The vacuum generated by secondejector 206 may be routed to conduit 84 and/or through vent valve 204.Control of flow through second ejector 206 may be provided by ejectormotive flow control valve 208, which may be positioned either upstreamor downstream of second ejector 206.

Wastegate actuator vacuum may be controllable by either the motive flowvalve (e.g. 86, 208) or from vent valve 204, which either applies vacuumor venting of vacuum.

A vacuum reservoir 210 may be fluidically coupled to both ejector 80 andsecond ejector 206 and to wastegate actuator 44. As depicted in FIG. 2,a conduit from reservoir 210 as well as a conduit from second ejector206 intersect with and are fluidically coupled to conduit 84. Thus,vacuum from both reservoir 210 and second ejector 206 may be routed towastegate actuator 44. In this way, vacuum may be stored in reservoir210 and applied to wastegate actuator 44 if the pressure drop acrossejector 80 and/or second ejector 206 is not sufficient to control theposition of wastegate 42. Additionally, a first check valve 212 andsecond check valve 214 may prevent depletion of vacuum from reservoir210 and/or ensure vacuum only flows from ejector 80 or second ejector206 to wastegate actuator 44 and not the other direction. Similar toFIG. 1, air flow though the various conduits and passageways of enginesystem 200 are depicted by the arrows of FIG. 2.

The configuration depicted in FIG. 2 is not limiting, as otherconfigurations are possible. For example, reservoir 210 may be dispensedwith. Similarly, second ejector 206 may be dispensed with, and vacuumfrom intake manifold 24 may be supplied to conduit 84 and wastegateactuator 44 via a direct supply line coupled to the intake passage 18downstream of throttle 22. Further, while FIGS. 1 and 2 depict vacuumgenerated from the ejector in the compressor flow path and/or vacuumfrom the intake manifold being directed to a wastegate actuator, othervacuum consumers may receive the vacuum in addition to or alternativelyof the wastegate actuator. Example vacuum consumers include a brakebooster for the vehicle braking system, charge motion control valve,fuel vapor canister (in order to provide vacuum for purging fuel vaporsfrom the canister), and other vacuum-consuming devices.

Thus, the systems of FIGS. 1 and 2 provide for a system for an engine,comprising a compressor coupled to a turbine; an ejector positioned in abypass path of the compressor; a wastegate valve of the turbine actuatedby a vacuum actuator; and a vacuum conduit coupling the ejector to thevacuum actuator. The system may include a vent line coupling the vacuumconduit to an intake passage upstream of the compressor. A vent valvemay be positioned in the vent line, and the system may include acontroller including instructions to adjust the vent valve based ondesired boost pressure.

The system may include a second ejector positioned across a throttle andfluidically coupled to the vacuum conduit. A valve may be positioned inthe bypass path of the compressor. In one example of the system, acontroller may include instructions to open the valve based on mass airflow and compressor pressure ratio. In another example, the controllermay include instructions to open the valve based on desired boostpressure. A compressor bypass valve may be positioned parallel to theejector.

FIG. 3 shows another embodiment of a system for actuating a wastegatevalve with a vacuum-driven actuator. The system illustrated in FIG. 3uses vacuum generated from an engine exhaust to control a wastegateactuator, rather than vacuum generated from compressor bypass flow as inthe systems of FIGS. 1 and 2. FIG. 3 illustrates an engine system 300.Engine system 300 is similar to engine systems 10 and 200, in that itincludes an engine 12, compressor 90, turbine 92, wastegate 42, andwastegate actuator 44, as well as other components previously described.In engine system 300, wastegate actuator 44 is supplied vacuum byejector 302 positioned in an exhaust flow path. As shown, ejector 302 ispositioned in a bypass passage 304 that is parallel to bypass passage40. However, ejector 302 may be positioned in bypass passage 40 in someembodiments. Thus, ejector 302 receives exhaust flowing from the engine12 and outlets the exhaust to the exhaust passage 35 downstream of theturbine 92. The vacuum generated by ejector 302 is routed to wastegateactuator 44 via conduit 306. Thus, as the exhaust flow from the engineincreases, increasing turbine speed and thus boost pressure, the amountof vacuum supplied by the ejector 302 to the wastegate actuator 44 alsoincreases.

In this way, exhaust pressure may be used as the actuating pressurewithout placing the wastegate actuator in the exhaust flow path, whereit would be subject to high heat, thus compromising the diaphragm and/orpneumatic hose of the actuator. In the configuration illustrated in FIG.3, the boost pressure provides both the signal to open the wastegate aswell as the mechanism for generating the vacuum to open the wastegate.

While the ejector in FIG. 3 is shown be coupled across the turbine withthe turbine inlet acting as the high-pressure source to the ejector andthe turbine outlet acting the low-pressure sink, other configurationsare possible. For example, the ejector may receive high-pressure airfrom the turbine inlet and release air to the compressor inlet. Inanother example, the ejector may receive air from the turbine outlet andrelease air to downstream of the catalyst or to the compressor inlet.

In order to provide controllability of the wastegate actuation, a ventvalve may be interposed between wastegate actuator 44 and ejector 302.In a “vacuum” position, the valve may apply the full vacuum of ejector302. In the “vent” position, the valve may put atmospheric pressure oneach side of the vacuum actuator 44. The vent valve may always vent someflow in any position except full vacuum. In other examples, that thevent valve may include three modes: increase vacuum, vent vacuum away,and hold current vacuum. In any case, this valve allows control via thecontroller instead of strictly via pneumatic-mechanical adjustments.

FIG. 4 illustrates the vacuum-generation system of FIG. 3 with optionalactive boost control and wastegate actuation at low or no boostconditions. FIG. 4 illustrates an example engine system 400 thatincludes the wastegate actuator 44 and ejector 302 of FIG. 3, amongother components already described. Conduit 306, which couples ejector302 to wastegate actuator 44, runs the entire length from ejector 302 towastegate actuator 44, with additional lines and conduits explainedbelow intersecting with and coupled to conduit 306.

Reservoir 416 may be provided vacuum by four separate sources: ejectors302, 410, 406, and the intake manifold. Other ejector based sources arealso possible.

Ejector 302 results in introduction of air into the exhaust stream. Thisis an advantage in certain cases. One case is during catalyst light offwhere may function as a secondary air introduction pump. Another case isduring rich operation where added air reduces regulated emissions,albeit at the cost of increased catalyst heat.

In order to provide active boost control via actuation of wastegate 42,a vent line 402 may be present in order to couple conduit 306 to theintake passage 18 upstream of compressor 90. A vent valve 404 may bepositioned in vent line 402 or at the intersection of vent line 402 andconduit 306. Vent valve 404 may be controlled by controller 50 to adjustthe amount of vacuum supplied to wastegate actuator 44, with excessvacuum being routed back to the intake via the vent line 402. Thus, bycontrolling vent valve 404, active boost pressure control may beprovided.

In order to open wastegate 42 under conditions of little or no boost(e.g., when sufficient vacuum is not generated via ejector 302), vacuummay be routed to wastegate actuator 44 from the intake manifold 24. Toprovide intake manifold vacuum, a second ejector 406 may be coupledacross the throttle 22. Second ejector 406 may generate vacuum frommotive flow of intake air from upstream of the throttle to downstream ofthe throttle. The vacuum generated by second ejector 406 may be routedto conduit 306 and/or through vent valve 404. Control of flow throughsecond ejector 406 may be provided by ejector motive flow control valve408.

In some embodiments, a third ejector 410 may be present in thecompressor bypass flow passage, similar to the ejector 80 describedabove with respect to FIGS. 1 and 2. Vacuum from third ejector 410 maybe routed to conduit 306 via conduit 412. To control airflow throughthird ejector 410, an ejector motive flow control valve 414 may bepresent in the bypass passage housing third ejector 410.

A vacuum reservoir 416 may be fluidically coupled to ejector 302, secondejector 406, third ejector 410, and to wastegate actuator 44. Asdepicted in FIG. 4, a conduit from reservoir 416, conduit 412 from thirdejector 410, as well as a conduit from second ejector 406 intersect withand are fluidically coupled to conduit 306. Thus, vacuum from reservoir416, third ejector 410, and/or second ejector 406 may be routed towastegate actuator 44. In this way, vacuum may be stored in reservoir416 and applied to wastegate actuator 44 if the pressure drop acrossejector 302, third ejector 410, and/or second ejector 406 is notsufficient to control the position of wastegate 42. Additionally, afirst check valve 418, second check valve 420, and third check valve 422may prevent depletion of vacuum from reservoir 416 and/or ensure vacuumonly flows from ejector 302, second ejector 406, or third ejector 410 towastegate actuator 44 and not the other direction. Similar to previousfigures, air flow though the various conduits and passageways of enginesystem 400 are depicted by the arrows of FIG. 3.

Under conditions of high intake manifold vacuum, flow air through secondejector 406 may not be needed to generate sufficient vacuum to actuatewastegate 42. Thus, a direct passage 424 may couple intake passage 18upstream of intake manifold 24 to conduit 306. A fourth check valve 426may be present in direct passage 424.

The configuration depicted in FIG. 4 is not limiting, as otherconfigurations are possible. For example, reservoir 416 may be dispensedwith. Similarly, second ejector 406 and/or third ejector 410 may bedispensed with. Further, while FIGS. 3 and 4 depict vacuum generatedfrom the ejector in the exhaust flow path and/or vacuum from the intakemanifold being directed to a wastegate actuator, other vacuum consumersmay receive the vacuum in addition to or alternatively of the wastegateactuator. Example vacuum consumers include a brake booster for thevehicle braking system, charge motion control valve, fuel vapor canister(in order to provide vacuum for purging fuel vapors from the canister),and other vacuum-consuming devices.

The systems illustrated in FIGS. 3 and 4 provide for a system for anengine, comprising a compressor positioned in an intake of the engineand coupled to a turbine positioned in an exhaust of the engine; anejector positioned in an exhaust flow path; a wastegate valve of theturbine actuated by a vacuum actuator; and a vacuum conduit coupling theejector to the vacuum actuator. An inlet of the ejector may bepositioned in the exhaust flow path upstream of the turbine and anoutlet of the ejector may be positioned in the exhaust flow pathdownstream of the turbine. In other examples, the ejector inlet may bepositioned in the exhaust upstream of the turbine and the ejector outletmay be positioned in an intake upstream of the compressor.

The system may further comprise a vent line coupling the vacuum conduitto an intake passage upstream of the compressor. A vent valve may bepositioned in the vent line, and a controller may include instructionsto adjust the vent valve based on desired boost pressure. The system mayinclude a second ejector positioned across a throttle and fluidicallycoupled to the vacuum conduit. A third ejector may be positioned acrossthe compressor and fluidically coupled to the vacuum conduit.

Thus, the systems provided in FIGS. 1 and 2 provide for actuating awastegate with vacuum generated by an ejector positioned in a compressorbypass flow path, while the systems of FIGS. 3 and 4 provide foractuating the wastegate with vacuum generated by an ejector positionedin an exhaust flow path. Each wastegate actuation system may include avent line and vent valve controllable by the controller to supply aselected amount of vacuum to the actuator, thus providing boost control.Further, each actuation system may include an additional vacuum source,originating from intake manifold vacuum, to supply vacuum to theactuator during low or no boost conditions.

FIG. 5 illustrates a method 500 for supplying vacuum to a vacuumactuator, such as wastegate actuator 44 of FIGS. 1-4. Method 500 may becarried out by controller 50 according to instructions stored thereon.Method 500 comprises, at 502, determining operating parameters.Operating parameters may include engine speed and load, boost pressure(as determined by compressor inlet pressure (CIP), throttle inletpressure (TIP), and/or MAP), and other parameters. At 504, it isdetermined if the engine is operating with boost (e.g., MAP greater thanbarometric pressure). If the engine is not operating with boost, whichmay occur during light load operation for example, method 500 proceedsto 506 to open a wastegate positioned across a turbocharger turbine byapplying vacuum to the wastegate actuator. As indicated at 508, thevacuum may be routed from the intake manifold to the wastegate actuator,for example by opening valve 208 of FIG. 2 or opening valve 408 of FIG.4. The vacuum may be supplied directly from the intake manifold (orintake passage upstream of the manifold and downstream of the throttle),or it may be generated by flowing the intake air through an ejectorcoupled across the throttle. However, in some examples, vacuum may berouted from a vacuum reservoir instead of the intake manifold. Byopening the wastegate even in unboosted conditions, pumping lossesthrough the turbine may be reduced, thus increasing fuel economy. Method500 then returns.

If it is determined at 504 that the engine is operating with boost,method 500 proceeds to 510 to determine if a desired amount of boost isdifferent than a provided amount of boost. The desired amount of boostmay be based on engine speed and load, in one example. If the desiredamount of boost and provided amount of boost are not different, noadjustments to the current wastegate position are indicated, and thusmethod 500 proceeds to 512 to maintain current operating parameters(e.g., maintain current wastegate position), and then method 500returns.

Returning to 510, if the desired amount of boost and the provided amountof boost are different, method 500 proceeds to 514 to adjust thewastegate position by applying vacuum to the wastegate actuator. Toapply the vacuum, at 516, a position of the vent valve may be adjustedto provide a desired amount of vacuum to the wastegate actuator toadjust the wastegate position. The desired amount of vacuum may be basedon the desired boost pressure. Depending on the configuration of theactuation system, the vacuum may be supplied to the wastegate actuatorfrom various sources. As indicated at 518, vacuum may be routed from thecompressor bypass flow path to the actuator when boost is relativelyhigh and/or intake manifold vacuum is relatively low. Further, in someexamples, the ejector motive flow control valve in the compressor bypassflow may be opened to provide the motive flow through the ejector togenerate the vacuum. If the ejector is positioned in the compressorbypass flow, as illustrated in FIGS. 1 and 2, vacuum may be generated bythe ejector when boost is above a threshold. The threshold amount ofboost may be no boost, so that vacuum is supplied to the actuator anytime boost is available. In other embodiments, the threshold may be thedesired amount of boost, and if excess boost is available above thedesired amount, then vacuum may be generated by the ejector and suppliedto the actuator. In still other embodiments, the threshold may be fixedamount of boost that provides enough vacuum generation to actuate thewastegate. Generation of vacuum through the compressor bypass ejectormay be actively controlled by opening valve 86, or it may occurpassively when provided boost is higher than desired boost. Further, thewastegate position may be selected in order to maintain some excessboost for generating the vacuum. However, in other examples, thewastegate position may be selected to bring the provided boost to thelevel of the desired boost, even if excess boost is subsequently notavailable for vacuum generation.

If the ejector is positioned in the exhaust flow, as illustrated inFIGS. 3 and 4, vacuum may be routed from the exhaust flow to theactuator when boost is high and/or manifold vacuum is low, as indicatedat 520. The conditions for routing vacuum from the exhaust flow may besimilar to those for routing vacuum from the compressor bypass flow, inthat a sufficient amount of boost needs to available to generate thevacuum. Further, in some examples, the ejector motive flow control valvein the exhaust flow path may be opened to provide the motive flowthrough the ejector to generate the vacuum.

If boost pressure is too low to generate sufficient vacuum (for both thecompressor bypass ejector and the exhaust ejector), and if manifoldvacuum is high, vacuum may be routed from the intake manifold to theactuator, as indicated at 522. The routing of vacuum from the intakemanifold may be similar to that described above at 506 and 508. However,in some embodiments, vacuum may be routed from a vacuum reservoirinstead of the intake manifold.

Thus, method 500 of FIG. 5 provides for actuating a wastegate using avacuum actuator during both higher boost and lower boost conditions. Inone example, a method for an engine including a turbocharger having acompressor driven by a turbine comprises generating vacuum viacompressor bypass flow through an ejector, and applying vacuum from theejector to a wastegate actuator. Another method for an engine includinga turbocharger having a compressor driven by a turbine comprisesgenerating vacuum via exhaust flow through an ejector, and applyingvacuum from the ejector to a wastegate actuator.

For both the methods, the wastegate actuator may be configured to adjusta wastegate valve of the turbine. The vacuum from the ejector to thewastegate actuator may be supplied via a conduit fluidically couplingthe ejector to the wastegate actuator, and a vent line may fluidicallycouple the conduit to an intake passage upstream of the compressor.

The methods may further comprise adjusting boost pressure by adjusting avalve positioned in the vent line. The methods may also compriseapplying vacuum from an intake manifold of the engine to the wastegateactuator. Applying vacuum from the intake manifold of the engine to thewastegate actuator may further comprise generating vacuum via a secondejector positioned in an intake flow path. The methods may includestoring vacuum generated by the ejector and/or the second ejector in avacuum reservoir.

In another example, a method for an engine including a turbochargerhaving a compressor driven by a turbine comprises during a firstcondition, adjusting a wastegate valve of the turbine via a vacuumactuator with vacuum received from an ejector positioned in a compressorbypass flow pathway, and during a second condition, adjusting thewastegate valve via the vacuum actuator with vacuum received from anintake manifold of the engine. An additional method for an engineincluding a turbocharger having a compressor driven by a turbinecomprises during a first condition, adjusting a wastegate valve of theturbine via a vacuum actuator with vacuum received from an ejectorpositioned in an exhaust flow pathway, and during a second condition,adjusting the wastegate valve via the vacuum actuator with vacuumreceived from an intake manifold of the engine.

For the methods, the first condition may comprise boost pressure above athreshold and the second condition may comprise boost pressure below thethreshold. In another example of the methods, the first condition maycomprise intake manifold vacuum below a threshold and the secondcondition may comprise intake manifold vacuum above the threshold.

The methods may further comprise adjusting boost pressure by adjusting avent valve positioned in a vent line fluidically coupling the ejector toan intake passage upstream of the compressor. Adjusting the wastegatevalve via the vacuum actuator with vacuum received from the intakemanifold may further comprise adjusting the wastegate valve via thevacuum actuator with vacuum received from a second ejector positionedacross a throttle of the intake manifold.

A motive flow control valve in the exhaust flow path may be opened togenerate vacuum from the ejector, when the ejector is positioned in theexhaust flow path. When the ejector is positioned in the compressorbypass flow path, a motive flow control valve in the compressor bypassflow path may be opened to generate vacuum from the ejector.

Returning briefly to FIG. 2, the two ejectors illustrated in FIG. 2(ejector 80 and second ejector 206) may receive motive flow that iscontrolled by two separate valves (motive flow control valve 86 andmotive flow control valve 208), each having their own separate actuatorsto allow for independent control of the motive flow through eachejector. However, such actuators may be expensive. Further, in typicalejector systems, air exiting the ejector is routed to one or more lowpressure sinks (e.g., intake manifold) via high-flow check valves, whichare also expensive. To eliminate the usage of the high-flow check valvesin the motive flow path, multiple ejectors may be used (e.g., oneejector for each low pressure sink), as illustrated in FIG. 2.Additionally, a single actuator may be used to control the position ofboth motive flow control valves. Such a configuration is illustrated inFIGS. 6 and 7, described below.

FIG. 6 illustrates an engine system 600 including an intake manifold 24,compressor 90, throttle 22, and other components described in theprevious figures. Although not shown in FIG. 6, intake manifold 24 iscoupled to an engine, similar to the intake manifolds illustrated inFIGS. 1-4. Engine system 600 includes two ejectors, first ejector 602and second ejector 604. First ejector is positioned in a bypass passage606 that is coupled to the intake passage across throttle 22; air entersbypass passage from upstream of intercooler 26 (although it mayalternatively enter the passage from downstream of intercooler 26 andupstream of throttle), travels though first ejector 602, and exits tothe intake manifold 24. A first motive flow control valve 608 ispositioned in bypass passage 606.

Second ejector 604 is located in bypass passage 610, which bypasses thecompressor 90. Air enters bypass passage 610 from the compressor outlet,travels though second ejector 604, and exits to the compressor inlet. Asecond motive flow control valve 612 is positioned in bypass passage610. While FIG. 6 illustrates a separate compressor bypass valve 30 forcontrolling flow around the compressor, in some embodiments, thecompressor bypass valve may be replaced by the second motive flowcontrol valve 612. As discussed previously, compressor bypass valve 30may provide boost control as well as surge protection. Compressor surgeoccurs during conditions of high boost pressure (e.g., high pressureratio across the compressor) and low air flow through the compressor;compressor surge may result in degradation to the turbochargercomponents in some conditions. Thus, to reduce surge, air from thecompressor outlet may be routed back to the compressor inlet via thecompressor bypass valve, thus increasing flow through the compressor andreducing surge. Alternatively, cooled, post—charge air cooler air may becirculated around the compressor to improve the surge margin. Ifcompressor bypass valve 30 is dispensed with, second valve 612 may actas a surge margin valve, being opened during surge conditions to providesurge protection. During conditions of turbo spin up, such as duringvehicle acceleration, second valve 612 may be closed. By replacing thecontinuously variable compressor bypass valve with the on/off secondvalve 612, comprise of the turbo spin up by the “permanent leak”introduced by the continuously variable compressor bypass valve may bereduced.

First valve 608 and second valve 612 may be actuated by a commonactuator 614. Actuator 614 may be a solenoid actuator that is activatedupon receiving current from controller 50. Actuator 614 may have adefault position that resumes when not activated. In the defaultposition, one of the valves may be closed while the other may be open.In the activated position, the closed valve opens and the open valvecloses. For example, with the actuator in the default position, firstvalve 608 may be open while second valve 612 may be closed. In theactivated position, first valve 608 may close while second valve 612 mayopen. In this way, a single actuator may be used to control the positionof multiple flow control valves. FIG. 6 illustrates the valves 608, 612as inline valves, however other valve configurations are possible. Forexample, the valves may be gate valves positioned at the throats of theejectors. Further, the control line between actuator 614 and valve 608and valve 612 by which actuator 614 adjusts the position of the valvesis depicted as a dotted line in FIG. 6.

First ejector 602 and second ejector 604 may each direct vacuum to avacuum reservoir 616, which may be coupled to one or more vacuumconsumers 618 and 620. The vacuum consumers may be suitable devices thatutilize vacuum, such as pneumatic actuators (wastegate actuator, CMCVactuator, brake booster, engine mounts, front axle disconnect, HVACcontrols, etc.) and/or gas ingestion systems/devices (for ingestinggaseous fuel, crankcase gases, circulated exhaust, and fuel vapors, forexample).

While FIG. 6 shows two valves actuated by a single actuator, in someembodiments the two valves may be replaced with a single valve. As shownin FIG. 7, an engine system 700, similar to system 600, includes bypasspassages 606 and 610 sharing a common intake line 702 that leads to avalve 704. Valve 704 may be actuated by an actuator to one of twopositions. When the actuator is in a first, default position, the valve704 may be a first position where air from intake line 702 is routedthrough first ejector 602, while when the actuator is a second,activated position, the valve 704 may be moved into a second positionwhere air is routed from intake line 702 through second ejector 604.

Both FIGS. 6 and 7 depict coordinated control of air flow through twoejectors, such that when air flows through one ejector, it does not flowthrough the other ejector. Because one ejector receives motive flowduring conditions of high boost (second ejector 604), while the otherreceives motive flow during conditions of high intake manifold vacuum,vacuum generation by the ejectors may be produced during most operatingconditions, and may be as effective as when the ejectors areindependently controlled.

The systems of FIGS. 6 and 7 provide for a system for an enginecomprising a first ejector positioned across a throttle and controlledby a first valve; a second ejector positioned in a compressor bypassflow and controlled by a second valve; and a common actuator configuredto simultaneously adjust a position of the first valve and the secondvalve. The second valve may comprise a continuously variable compressorbypass valve. The system may include controller with instructions toactivate the common actuator to open the second valve and close thefirst valve when boost pressure is above a threshold. The controller mayalso include instructions to activate the common actuator to open thesecond valve and close the first valve in response to compressoroperation in a surge region, wherein compressor pressure ratio is abovea threshold and compressor flow rate is below a threshold. Thecontroller may include instructions to activate the common actuator toclose the second valve and open the first valve in response to turbolag, wherein desired boost to provide engine power demand exceedsprovided boost by more than a threshold amount.

Turning now to FIG. 8, a method 800 for generating vacuum with multipleejectors having separate motive flow control valves actuated by a commonactuator is illustrated. Method 800 may be carried out by controller 50according to instructions stored thereon, in order to generate vacuum inengine system 600 of FIG. 6 or engine system 700 of FIG. 7. Method 800includes, at 802, generating vacuum via a first ejector with an actuator(e.g., actuator 614) in a default, first position. As explainedpreviously, the actuator may have a default position that the actuatorassumes when it is not activated. The first ejector may be positioned inan intake air flow path, across a throttle, such as first ejector 602.As indicated at 804, the intake air flows through the first ejector togenerate the vacuum. Further, with the actuator in the first position, afirst motive flow control valve (e.g., first valve 608) is open and asecond motive flow control valve (e.g., second valve 612) is closed, asindicated at 806. Thus, air flows through the first valve to the firstejector with the actuator in the first position, but does not flowthrough the second valve to the second ejector.

At 808, engine operating parameters are determined. The determinedengine operating parameters may include boost pressure, engine speed andload, MAP, and other parameters. At 810, it is determined if boostpressure is above a threshold. The threshold boost pressure may be noboost, so that any boost is above the threshold. In other embodiments,the threshold may be desired boost, or may be a fixed amount of boost.If boost pressure is above the threshold, method 800 proceeds to 816,which will be explained below. If boost pressure is not above thethreshold, method 800 proceeds to 812 to maintain the actuator in thedefault position, as sufficient boost pressure is not available togenerate vacuum with the second ejector.

Method 800 proceeds to 814 to determine if the compressor is currentlyoperating or predicted to operate in a surge region. Compressor surgemay result from low air flow through the compressor; under certainconditions, such as a driver tip-out event, the flow rate and pressureratio across the compressor can fluctuate to levels that may result innoise disturbances, and in more severe cases, performance issues andcompressor degradation. To mitigate such surge events, if the secondvalve has replaced the CBV, it may be opened to increase flow throughthe compressor. As used herein, the term “surge region” includescompressor operating points that result in surge (beyond a surge level,for example) as well as operating points near a surge level that do notresult in surge (but that may push the compressor to surge when smallair flow fluctuations occur). Additionally, the compressor may beconsidered to be operating in the surge region if it is predicted thatthe compressor would enter surge at or while transitioning to the nextrequested operating point.

The surge region of the compressor is a function of compressor pressureratio (e.g., boost pressure) and air flow through the compressor. Thepressure ratio and air flow through the compressor may be mapped to acompressor operating map, which indicates if the compressor is operatingat surge. Alternatively, compressor operation in the surge region may bedetermined based on engine speed and load. Further, even if thecompressor is not currently operating with surge, subsequent operationwith surge may be predicted based on the next requested operating point.For example, if a tip-out event or other drop in engine speed or loadhas occurred, it may be predicted that the air flow through thecompressor is about to decrease, and thus it may be estimated that thecompressor is going to operate in the surge region.

If the compressor is not operating in the surge region (or is notpredicted to operate in the surge region), method 800 returns to 812 tomaintain the default actuator position. If the compressor is operatingor predicted to operate in the surge region, method 800 proceeds to 816to activate the solenoid of the actuator to adjust the actuator to asecond position and generate vacuum via a second ejector (e.g., secondejector 604). Additionally, as explained above, if at 810 it isdetermined that boost pressure is above the threshold, method 800 alsoproceeds to 816 to activate the solenoid.

With the solenoid activated and the actuator in the second position,compressor bypass air flows through the second ejector to generate thevacuum, as indicated at 818. To flow air through the second ejector, theactuator opens the second valve and closes the first valve, as indicatedat 820.

At 822, it is determined if boost pressure drops below the threshold, orif turbo lag is detected. Turbo lag refers to a condition where theamount of provided boost is not sufficient to meet engine power demands,and may occur during a tip-in event or vehicle acceleration. Turbo lagmay cause a temporary, undesired lag in engine power that is noticeableto a vehicle operator. To mitigate the turbo lag, all exhaust in theexhaust passage may be routed through the turbine to quickly spin theturbine up to desired speed to produce the requested boost, and allintake air may be routed through the compressor. Thus, if turbo lag isdetected (or if it is predicted turbo lag is about to occur) or if boosthas dropped below the threshold, method 800 proceeds to 824 todeactivate the solenoid to return the actuator to the default position.

While method 800 of FIG. 8 describes control of two ejectors by twovalves with a single actuator, the two ejectors may be alternatively becontrolled by a single valve, as illustrated in FIG. 7. In such aconfiguration, the actuator may move the valve between a first positionwhere the first ejector is used to create vacuum and a second positionwhere the second ejector is used to create vacuum.

FIGS. 9 and 10 illustrate example engine operating conditions withcoordinated control of the two ejector motive flow control valves. FIG.9 illustrates a diagram 900 showing operating conditions during a steadystate cruise condition, with a vehicle traveling at constant enginepower. Curve 902 illustrates throttle inlet pressure (TIP), curve 904illustrates MAP, and curve 906 illustrates barometric pressure, withtime on the horizontal axis and pressure on the vertical axis. When TIPis above MAP, more efficient vacuum generation may occur with the secondejector, and thus as shown by curve 9010, the second valve is openduring a majority of the time illustrated in diagram 900. However,between times t1 and t2, TIP and MAP may become close enough that vacuumgeneration by the first ejector is preferred, and thus the first valve,illustrated by curve 908, is open during this time. As shown by curves908 and 910, when the first valve is open, the second valve is closed,and when the first valve is closed, the second valve is open.

FIG. 10 illustrates a diagram 1000 showing the same operating parametersas FIG. 9, during an acceleration event where the engine power demand isat or above provided air flow. TIP is illustrated by curve 1002, MAP isillustrated by curve 1004, BP is illustrated by curve 1006, the firstvalve position is illustrated by curve 1008, and the second valveposition is illustrated by curve 1010. Prior to time t1, TIP is greaterthan MAP, and thus the second valve may be open with the first valveclosed. After time t1, however, TIP is close to or at MAP, and thus thefirst valve is opened and the second valve is closed.

Thus, the systems and methods described herein provide for a method,comprising when boost is below a threshold, generating vacuum with anactuator in a first position by flowing air from a compressor outlet toan intake manifold through a first ejector, and when boost is above thethreshold, generating vacuum with the actuator in a second position byflowing air from the compressor outlet to a compressor inlet through asecond ejector. Generating vacuum with the actuator in the firstposition may further comprise opening a first valve and closing a secondvalve with the actuator in order to flow air through the first ejector.Generating vacuum with the actuator in the second position may furthercomprise closing the first valve and opening the second valve with theactuator in order to flow air through the second ejector.

The method may further comprise, in response to current or predictedcompressor operation in a surge region, closing the first valve andopening the second valve with the actuator and flowing air from thecompressor outlet to the compressor inlet through the second ejector.The method may also include in response to current or predictedturbocharger lag, opening the first valve and closing the second valvewith the actuator. Vacuum generated by the first ejector and the vacuumgenerated by the second ejector may be directed to a vacuum actuator.The vacuum actuator may comprise one or more of a wastegate actuator,brake booster, and charge motion control valve. The vacuum generated bythe first ejector and the vacuum generated by the second ejector may bedirected to an engine gas ingestion device. The engine gas ingestiondevice may comprise one or more of a fuel vapor canister, enginecrankcase, and intake manifold.

In another example, a method comprises during a first condition,generating vacuum via a first ejector by opening a first valve andclosing a second valve with a common actuator and flowing air from acompressor outlet to an intake manifold through the first ejector, andduring a second condition, generating vacuum via a second ejector byclosing the first valve and opening the second valve with the commonactuator and flowing air from the compressor outlet to a compressorinlet through the second ejector.

In an example, the first condition may comprise boost pressure above athreshold, and the second condition may comprise boost pressure belowthe threshold. In another example, the first condition may comprisecurrent or predicted compressor operation in a surge region, and thesecond condition may comprise current or predicted turbocharger lag. Themethod may further comprise determining if the current or predictedcompressor operation is in the surge region based on mass air flow rateand a level of provided boost. Current or predicted turbocharger lag maybe determined based on a difference between desired boost pressure andactual boost pressure. The method may include directing the vacuumgenerated by the first ejector and the vacuum generated by the secondejector to a vacuum reservoir, the vacuum reservoir coupled to one ormore vacuum consumers.

It will be appreciated that the configurations and methods disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for an engine including a turbocharger having a compressor driven by a turbine, comprising: generating vacuum via compressor bypass flow through an ejector; and applying vacuum from the ejector to a wastegate actuator; wherein the vacuum from the ejector to the wastegate actuator is supplied via a conduit fluidically coupling the ejector to the wastegate actuator, and wherein a vent line fluidically couples the conduit to an intake passage upstream of the compressor.
 2. The method of claim 1, wherein the wastegate actuator is configured to adjust a wastegate valve of the turbine.
 3. The method of claim 1, further comprising adjusting boost pressure by adjusting a valve positioned in the vent line.
 4. The method of claim 1, further comprising applying vacuum from an intake manifold of the engine to the wastegate actuator, wherein applying vacuum from the intake manifold of the engine to the wastegate actuator further comprises generating vacuum via a second ejector positioned in an intake flow path.
 5. The method of claim 4, further comprising storing vacuum generated by the ejector and/or the second ejector in a vacuum reservoir.
 6. A method for an engine including a turbocharger having a compressor driven by a turbine, comprising: during a first condition, adjusting a wastegate valve of the turbine via a vacuum actuator with vacuum received from an ejector positioned in a compressor bypass flow pathway; and during a second condition, adjusting the wastegate valve via the vacuum actuator with vacuum received from an intake manifold of the engine, wherein adjusting the wastegate valve via the vacuum actuator with vacuum received from the intake manifold further comprises adjusting the wastegate valve via the vacuum actuator with vacuum received from a second ejector positioned across a throttle of the intake manifold.
 7. The method of claim 6, wherein the first condition comprises boost pressure above a threshold and the second condition comprises boost pressure below the threshold.
 8. The method of claim 6, wherein the first condition comprises intake manifold vacuum below a threshold and the second condition comprises intake manifold vacuum above the threshold.
 9. The method of claim 6, further comprising adjusting boost pressure by adjusting a vent valve positioned in a vent line fluidically coupling the ejector to an intake passage upstream of the compressor.
 10. A system for an engine, comprising: a compressor coupled to a turbine; an ejector positioned in a bypass path of the compressor; a wastegate valve of the turbine actuated by a vacuum actuator; a vacuum conduit coupling the ejector to the vacuum actuator; and a compressor bypass valve positioned in parallel to the ejector.
 11. The system of claim 10, further comprising a vent line coupling the vacuum conduit to an intake passage upstream of the compressor.
 12. The system of claim 11, further comprising a vent valve positioned in the vent line and a controller including instructions to adjust the vent valve based on desired boost pressure.
 13. The system of claim 10, further comprising a second ejector positioned across a throttle and fluidically coupled to the vacuum conduit.
 14. The system of claim 10, further comprising a valve positioned in the bypass path of the compressor.
 15. The system of claim 14, further comprising a controller including instructions to open the valve based on mass air flow and compressor pressure ratio.
 16. The system of claim 14, further comprising a controller including instructions to open the valve based on desired boost pressure. 